Remove Python 3.6 branches from typeshed (#8269)

stdlib/http/cookies.pyi

@@ -30,11 +30,7 @@ class Morsel(dict[str, Any], Generic[_T]):
     @property
     def key(self) -> str: ...
     def __init__(self) -> None: ...
-    if sys.version_info >= (3, 7):
-        def set(self, key: str, val: str, coded_val: _T) -> None: ...
-    else:
-        def set(self, key: str, val: str, coded_val: _T, LegalChars: str = ...) -> None: ...
-
+    def set(self, key: str, val: str, coded_val: _T) -> None: ...
     def setdefault(self, key: str, val: str | None = ...) -> str: ...
     # The dict update can also get a keywords argument so this is incompatible
     @overload  # type: ignore[override]